<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>exercise</title>
    <style>
        #nav{
            width: 500px;
            height: 50px;

            background-color: orange;
        }
        #nav a{
            text-decoration: none;
            color:black;
            width: 160px;
            height: 50px;
           
            

        }
        #nav a:hover{
            color:green;
            background-color:pink;
        }
    </style>
</head>
<body>
    <div id="nav">
        <a  href="http://www.baidu.com">百度</a>
        <a href="#">淘宝</a>
        <a href="#">天猫</a>
        <a href="#">京东</a>
    </div>
    <div id="main">
        <a href="#">主体超链接</a>
    </div>
</body>
</html>